Resin coated copper powder for electroconductive paints

ABSTRACT

A process for preparing a copper powder for electroconductive paints, which comprises adding to a dispersion bath of copper powder and a dispersion medium a mixture of a titanium acylate polymer and a higher carboxylic acid ester to form a film of the titanium acylate polymer and the higher carboxylic acid ester on the surfaces of the particles of said copper powder, and if necessary, removing the dispersion medium to obtain the copper powder for electroconductive paints. The copper powder thus obtained is coated on the surfaces of its particles with the titanium acylate polymer and the higher carboxylic acid ester.

BACKGROUND OF THE INVENTION

This invention relates to copper powder for electroconductive paints,more particularly to a copper powder for electroconductive paints(hereinafter referred to as conductive paint(s)) which has improvedstorage stability and environmental resistance and improves the adhesionof a paint film in which it is used without reduction of theconductivity of the copper powder and its shielding effect againstelectromagnetic waves. The invention relates also to a process forpreparing the copper powder.

One of the electromagnetic wave shielding materials known heretofore forthe purpose of protecting electronic equipments from disturbance orjamming by electromagnetic waves is a conductive paint in which aconductive filler such as nickel powder, silver powder, copper powder,or carbon powder is kneaded with any of various binder resins such asthermoplastic resins. Shielding against electromagnetic waves isaccomplished by applying the paint on the surface of molded articles byspraying or brushing. Conductive paints of copper type are inexpensivein comparison with those of silver or nickel types and have excellentshielding effect.

However, in the conductive paints of copper type, a uniform dispersionstate cannot be realized because the copper particles tend toagglomerate together in the paint, which leads to inferior storagestability. Moreover, the conductive paints of copper type tend to beeasily oxidized by environmental factors such as heat and humidity,which easily cause deterioration of environmental resistance andconductivity (attenuation of shielding effect) of the copper powder.Many methods have hitherto been proposed for the purpose of solvingthese problems. The methods include the preparation of conductive paintsby blending a binder resin and an organic titanate into copper powder(Japanese Patent Laid-Open Application No. 36553/81), the surfacetreatment of copper powder with a coupling agent (Japanese PatentLaid-Open Application No. 30200/85), coating of the particles ofelectrolytic copper powder with an organic titanate (Japanese PatentLaid-Open Application No. 174661/84), coating of the particles of copperpowder with an organic aluminum (Japanese Patent Laid-Open ApplicationNo. 179671/84) and the like.

The conductive paints thus obtained with copper powder are improved to acertain extent in storage stability and environmental resistance withouta decrease in the conductivity of the copper powder and its shieldingeffect against electromagnetic waves.

However, conductive paints obtained with copper powder in the prior art,when used by the application thereof onto a substrate or matrix, areinferior in adhesion to the substrate and do not always exhibitexcellent storage and environmental resistance.

This invention has been achieved in view of the above describedbackground. An object of this invention is to overcome the problemsaccompanying conventional copper powders for conductive paints and toprovide a copper powder for conductive paints which has improved storagestability and environmental resistance as well as the effect ofimparting good adhesion to the paint film without reduction of theconductivity of the copper powder and shielding effect with respect toelectromagnetic waves. Another object is to provide a process forpreparing the copper powder according to the invention.

SUMMARY OF THE INVENTION

We have conducted a variety of researches on copper powder forconductive paints. As a result, it has been found that a paintcontaining copper powder exhibits excellent adhesion to a substrate ormatrix if the surfaces of the particles of the copper powder are coatedwith a mixture of a titanium acylate polymer and a higher carboxylicacid ester. The present invention has been achieved on the basis of thisdiscovery.

In other words, the copper powder for conductive paints according tothis invention is characterized in that the surfaces if its particlesare coated with a titanium acylate polymer and a higher carboxylic acidester.

In a preferred embodiment of this invention, the higher carboxylic acidester is a fatty acid ester having 10 to 24 carbon atoms and thetitanium acylate polymer has repeating units represented by thefollowing formulae I, II and /or III: ##STR1## wherein: R, R₁, R₂ and R₃may be the same or different and represent hydrocarbon groups having 1to 25 carbon atoms; preferably R represents a hydrocarbon group having 1to 5 carbon atoms; and R₁, R₂ and R₃ represent hydrocarbon groups having10 to 24 carbon atoms.

The process for preparing a copper powder for conductive paintsaccording to this invention is characterized in that a mixture of atitanium acylate polymer and a higher carboxylic acid ester is added toa dispersion bath of the copper powder and a dispersion medium to form afilm of the titanium acylate polymer and the higher carboxylic acidester on the surfaces of the particles of the copper powder, and ifnecessary, the dispersion medium is removed to obtain the copper powderfor conductive paints.

In a preferred embodiment of this invention, the titanium acylatepolymer and the higher carboxylic acid ester are mixed in a ratio of 40to 80% by weight of the titanium acylate polymer to 60 to 20% by weightof the higher carboxylic acid ester, and the mixture of the titaniumacylate polymer and the higher carboxylic acid ester is a reactionmixture of a tetraalkoxytitanium with an alkyl group having 1 to 10carbon atoms and a higher carboxylic acid.

In a preferred embodiment of this invention, the mixture of the titaniumacylate polymer and the higher carboxylic acid ester is a reactionmixture of 1 mole of a tetraalkoxytitanium and 2 to 5 moles, morepreferably 3 to 4 moles of a higher carboxylic acid.

According to this invention and the preferred embodiment, the followingprocess is conducted:

When the mixture of the titanium acylate polymer and the highercarboxylic acid ester is to be obtained from a reaction mixture of atetraalkoxytitanium Ti(OR)₄ and a higher carboxylic acid R'COOH, thereaction proceeds as shown in the following reaction equations, whereinthe coefficients in the equations are abbreviated: ##STR2## wherein: Rrepresents an alkyl group; R" represents a hydrogen atom or a group R orCOR'; and n denotes a polymerization degree.

As shown above, the tetraalkoxytitanium is first acylated by the highercarboxylic acid to form a titanium acylate dimer, and the remaininghigher carboxylic acid and an alcohol formed s a by-product of acylationis reacted by the catalytic effect of the titanium compound to form acarboxylate ester. The titanium acylate dimer is condensed repeatedly toform a titanium acylate oligomer which is further polymerized to atitanium acylate polymer. Accordingly, a desirable mixture can beobtained from the reaction mixture of the tetraalkoxytitanium and thehigher carboxylic acid.

In the copper powder of this invention, the surfaces of the particles ofthe copper powder are coated with the mixture of the titanium acylatepolymer and the higher carboxylic acid ester. The hydrophobic film ofthe macromolecule titanium acylate polymer covers the surfaces of theparticles of the copper powder, but the coverage remains insufficient,so that gaps or cracking will be formed in the film. In such a gap isformed a hydrophobic film of the carboxylic acid ester, and finally adense film is formed on the surfaces of the particles of the copperpowder. Moreover, according to this invention, a higher carboxylic acidester is used, so that the thickness of the hydrophobic film in thedirection perpendicular to the surface of the copper powder can becontrolled and therefore made uniform.

Furthermore, by the application of the titanium acylate polymer and thehigher carboxylic acid ester as a coating on the surfaces of the copperpowder particles, a good dispersion state of the copper powder in thepaint and dried paint film can be obtained, and the adhesion withrespect to the substrate can be greatly improved.

When the surfaces of the particles of the copper powder are coated withthe mixture of the titanium acylate polymer and the higher carboxylicacid ester, the titanium acylate polymer is hydrolyzed at the alkoxygroup by the adsorption water on the surfaces of the particles of thecopper powder and is bonded to and arranged on the surface of the copperpowder. The carboxylic acid ester also reacts with the adsorption wateron the surfaces of the copper powder particles to undergo ester exchangereaction and is bonded to and arranged on the surfaces of the copperpowder particles. In this reaction, the carboxylic acid ester reactswith an alkoxy group or a terminal group in the titanium acylate polymermolecule which has been bonded to the surfaces of the copper powderparticles or with an alkoxy group or a terminal group in the unreactedtitanium acylate polymer molecule to suppress the condensation, wherebythe thickness of the hydrophobic film in the direction perpendicular tothe surface of the copper powder can be controlled and made uniform. Inaddition, the acylate group, a side chain of the titanium acylatepolymer bonded to and arranged on the surfaces of the copper particlesand the higher carboxylic acid ester of a long chain are entangled witha binder resin molecule in the paint and dry film by the van der Waalsforce, hydrogen bond, ionic bond, covalent bond and the like to form agood dispersion state of the copper powder, whereby uneven distributionof the copper powder is diminished, and the adhesion of the paint filmto the substrate is greatly improved.

As will be confirmed by the following examples, according to the copperpowder for conductive paints of this invention, it is possible to solvethe difficulties of the conventional copper powder for conductive paintsand to improve its storage stability and environmental resistance aswell as good adhesion of a paint film containing the powder withoutreduction of the conductivity of the copper powder and its shieldingeffect against electromagnetic waves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electron micrograph (×700) of a section of a dry film of aconductive paint prepared with the copper powder of this invention; and

FIG. 2 is an electron micrograph (×700) of a section of a dry film of aconductive paint prepared with a copper powder which is out of the scopeof this invention.

DETAILED DESCRIPTION OF THE INVENTION Copper Powder

The copper powder used in this invention is in a branched shape,particle or ball shape, respectively obtained from electrolysis,reduction and atomization methods, or in the shape of flakes which isobtained by further processing the powder by the use of a ball mill orthe like.

The copper powder used in this invention has a specific surface area of1.5 m² /g or less, preferably 1.0 m² /g or less, a particle sizedistribution of 1 to 100 μm, preferably 1 to 50 μm, and a mean particlediameter of 3 to 30 μm, preferably 5 to 15 μm. If the specific surfacearea exceeds 1.5 m² /g, the resistance to oxidation of copper powderwill be greatly lowered. If the particle size distribution departs fromthe range of 1 to 100 μm and the mean particle diameter departs from therange of 3 to 30 μm, a paint film exhibiting a uniform conductivitycannot be obtained, and the nozzle tip spraying the paint will beclogged.

It is also possible to use powders of branched shape, flakes, particlesand balls blended by a V type mixer or the like.

Another copper powder which may be used in this invention is copperpowder covered with silver. The amount of silver for covering is 0.1 to20% by weight, preferably 1.0 to 5.0% by weight with respect to that ofthe copper component. This is because the resistance to oxidation of thecopper powder is inferior with an amount of silver less than the lowerlimit, and the manufacturing cost will be increased if the amountexceeds the upper limit. If a copper powder covered with silver is used,a paint film having a shielding effect superior to that of a film withbare copper powder can be obtained, and thermosetting resins such asphenol resins, epoxy resins or the like as well as thermoplastic resinscan also be applied as a binder resin. Examples of the method forcovering the copper powder particles with silver are chemicalsubstitution plating method, CVD method, and mechanical bonding method.Other complex copper powders which can be used in this invention otherthan the copper powder covered with silver include, for example, copperpowders covered with metals such as nickel, zinc, palludium andplatinum.

It is preferable that the copper powder be pretreated according tonecessity, to remove the oxide layer from the surfaces of the copperpowder particles by the use of reagents such as mineral acids, organicacids, various kinds of reducing agents or by reduction with hydrogen.Furthermore, the copper powder to be treated can be dried as apre-treatment.

Titanium Acylate Polymer

One of the components to cover the copper powder particles according tothis invention is a titanium acylate polymer. Specifically, the polymeris a highmolecular weight compound which has the above mentionedrepeating unit I, II or III alone or any combination of the repeatingunits I, II, and III.

The titanium acylate polymer can be obtained by reacting atetraalkoxytitanium Ti(OR)₄ with a carboxylic acid, acid anhydride,inorganic acid or by reacting a tetrachlorotitanium Ti(Cl)₄ withammonia/carboxylic acid, sodium carboxylate or the like.

One preferred method for synthesizing titanium acylate polymers is themethod of reacting a tetraalcoxytitanium Ti(OR)₄ with a carboxylic acid,particularly with a higher fatty acid. In this method, by-products suchas chlorides, inorganic acids or the like are not produced. In addition,the side chain of the titanium acylate polymer is acylated by the use ofthe higher fatty acid to make the titanium acylate polymer film morehydrophobic, and the reaction products thus obtained can be used as anagent in the production of the copper powder of this invention.

Separation and purification of the synthesized titanium acylate polymercan be carried out with techniques such as distillation, extraction,recrystallization, column chromatography and the like.

Higher Carboxylic Acid Ester

The higher carboxylic acid esters in this invention have ong chaincarbon atoms, and the preferred ones include higher fatty acid estershaving 10 to 24 carbon atoms. Specific examples of such carboxylic acidesters are esters of higher saturated fatty acids such as stearic acidesters, palmitic acid esters, myristic acid esters, lauric acid esters,and capric acid esters, and isomers thereof and esters of higherunsaturated fatty acids such as oleic acid esters, linolic acid esters,and linoleic acid esters, and isomers thereof. If a lower carboxylicacid ester is used, the hydrophobicity of the carboxylic acid filmformed on the surface of the copper powder will be impaired and apreferred dispersion state of copper powder cannot be achieved duringthe formation of a paint or film in combination with binder resins.

The part of the ester corresponding to an alcohol comprises an alkoxygroup having 1 to 10 carbon atoms, preferably 1 to 5 carbon atoms.

Separation and purification of the synthesized carboxylic acid ester canbe carried out with techniques such as distillation, extraction,recrystallization, and column chromatography.

Process for Producing a Copper Powder for Conductive Paint

The process according to this invention comprises adding to a dispersionbath of copper powder and a dispersing medium a mixture of a titaniumacylate polymer and a higher carboxylic acid ester to form a film of thetitanium acylate polymer and of the higher carboxylic acid ester on thesurfaces of the copper powder particles and removing according tonecessity the dispersing medium to obtain the copper powder forconductive paint.

In the dispersion bath of the copper powder in this process, the copperpowder particles to be coated form a good dispersion state by means of adispersing medium. The dispersing medium in this case is, for example,water or an organic solvent such as an alcohol. Preferred dispersingmediums are water, methyl alcohol, ethyl alcohol, toluene, hexane andthe like. The amount of the dispersing medium is that necessary forforming the preferred dispersion state of the copper powder and ispreferably the minimal amount. If the amount of the dispersing mediumincreases, the reaction rate between the mixture of the titanium acylatepolymer and the higher carboxylic acid ester and the surfaces of thecopper powder particles is lowered, whereby it becomes difficult toobtain the desired copper powder.

The mixture of the titanium acylate polymer and higher carboxylic acidester to be added can be obtained by mixing certain amounts of the two,and it can also be obtained from the reaction mixture of atetraalkoxytitanium and a higher carboxylic acid.

The mixing ratio of the titanium acylate polymer and the highercarboxylic acid ester in this mixture is 5 to 95% by weight of thetitanium acylate polymer to 95 to 5% by weight of the higher carboxylicacid ester, preferably 40 to 80% by weight of the titanium acylatepolymer to 60 to 20% by weight of the higher carboxylic acid ester, morepreferably 40 to 60% by weight of the titaniumn acylate polymer to 60 to40% by weight of the higher carboxylic acid ester. If the amount of thetitanium acylate polymer is less than the above range, hydrophobicitywill be extremely inferior, and if the amount of the titanium acylatepolymer exceeds the upper limit, conductivity will be graduallydecreased. Also, if the amount of the higher carboxylic acid ester isless than the lower limit, dispersibility of the copper powder duringthe formation of the paint and film will be extremely poor.

The mixture of the titanium acylate polymer and the higher carboxylicacid ester can be diluted with, for example, organic solvents. Organicsolvents which can be used in this case are preferably non-polarsolvents such as toluene and hexane and polar solvents such as alcoholsand acetone.

In order to obtain the mixture of the titanium acylate polymer and thehigher carboxylic acid ester from the reaction mixture of atetraalkoxytitanium and a higher carboxylic acid, the mixture isobtained from 1 mole of the tetraalkoxytitanium and 2-5 moles of thehigher carboxylic acid, preferably from 1 mole of thetetraalkoxytitanium and 3-4 moles of the higher carboxylic acid. If theratio is less than the lower limit, a simple acylate such as amonoacylate or a titanium alkoxypolymer will be produced, but notitanium acylate polymer will be produced. On the other hand, if theratio is greater than the upper limit, the titanium acylate polymer willbe produced quantitatively but such by-products as carboxylic esters oralcohols are also produced excessively. The alkoxy group of thetetraalkoxytitanium used in this process has 1 to 10, preferably 1 to 5carbon atoms. If the number or the carbon atoms exceeds 5, hydrolysis ofthe compound with adsorption water on the surfaces of the copper powderparticles may not proceed rapidly, or the reactivity with the carboxylicacid for forming an acylate will be decreased. If the number exceeds 10,the reactivity decreases extremely to such a level that almost noreaction will occur.

The mixture of the titanium acylate polymer and the higher carboxylicacid ester is used in a proportion of 0.05 to 15% by weight, preferably0.1 to 10% by weight, more preferably 0.1 to 5% by weight relative tothe copper powder. If the mixture is used in an amount less than 0.1% byweight, the surfaces of the copper powder particles will beinsufficiently coated, whereby the copper powder particles will tend toagglomerate with each other, and the conductivity and shielding effectof the paint film will be very poor. On the other hand, if the amountexceeds 15% by weight, an excessive amount of the paint film will beformed, and good conductivity and shielding effect cannot be obtained.

The mixture of the titanium acylate polymer and the higher carboxylicacid ester is added to the dispersion bath of the copper powder directlyin small portions or after dilution thereof with an organic solvent orwater. Operation parameters such as addition rate and agitating timeafter addition are desirably selected according to the surface state ofthe copper powder, that is, the amount of adsorbed water, specificsurface area, shapes of the copper powder particles and the like.

After the film of the titanium acylate polymer and the higher carboxylicacid ester has been formed, the dispersing solvent is removed, ifnecessary. This is because, if the drying is insufficient, goodconductivity or shielding effect cannot be obtained because of theoxidation of the copper powder, and verdigris may be generated.

The copper powder thus obtained according to this invention can be mixedwith a binder resin and a solvent to form a conductive paintcomposition. In addition to the above components, a variety of additivescan be added depending on the intended use.

EXAMPLES

This invention will now be described more fully with respect to thefollowing examples, which are presented as illustrative only.

Experimental Materials a. Surface coating agent

A titanium acylate polymer (referred to hereinafter as TAP1) obtainedfrom 1 mole of tetraisopropyltitanium and 3 moles of isostearic acid andisopropyl isostearate (referred to hereinafter as ISA) were mixed inproportions as shown in Table 1 to form surface coating agents accordingto this invention.

                  TABLE 1                                                         ______________________________________                                        Surface                                                                       coating agent TAP1 (wt %)                                                                              ISA (wt %)                                           ______________________________________                                        1-1           50         50                                                   1-2           40         60                                                   1-3           60         40                                                   1-4           70         30                                                   1-5           90         10                                                   1-6           30         70                                                   ______________________________________                                    

A titanium acylate polymer (referred to hereinafter as TAP2) obtainedfrom 1 mole of tetraisopropyltitanium and 3 moles of palmitic acid andisopropyl palmitate (referred to hereinafter as PAI) were mixed inproportions as shown in Table 2 to form surface coating agents accordingto this invention.

                  TABLE 2                                                         ______________________________________                                        Surface                                                                       coating agent TAP2 (wt %)                                                                              PAI (wt %)                                           ______________________________________                                        2-1           50         50                                                   2-2           40         60                                                   2-3           60         40                                                   2-4           70         30                                                   2-5           90         10                                                   2-6           30         70                                                   ______________________________________                                    

For comparison, surface coating agents shown in Table 3 were also used.

                  TABLE 3                                                         ______________________________________                                        No.       Surface coating agent                                               ______________________________________                                        3-1       Isopropyltridodecylbenzenesulfonyltitanate                          3-2       Isopropyltris(dioctylpyrophosphate)titanate                         3-3       Bis(dioctylpyrophosphate)oxyacetatetitanate                         3-4       Tetraisopropylbis(dioctylphosphate)titanate                         3-5       Isopropyltricumylphenyltitanate                                     3-6       Isopropyltri(dioctylphosphate)titanate                              3-7       Bis(dioctylpyrophosphate)ethylenetitanate                           3-8       ν-methacryloxypropyltrimethoxysilane                             3-9       ν-glycidoxypropyltrimethoxysilane                                 3-10     ν-aminopropyltriethoxysilane                                      3-11     Acetoalkoxyaluminum diisopropylate                                  ______________________________________                                    

b. Copper powder

A branch-shaped electrolytic copper powder specified in Table 4 and aflake copper powder as specified in Table 5 which had been obtained fromspherical atomized copper powder by mechanical processing in a ball millwere used.

                  TABLE 4                                                         ______________________________________                                        Apparent density      0.8-1.1 g/cm.sup.3                                      Specific surface area 0.40 m.sup.2 /g                                         Purity                99.2% or more                                           Insolubles in HNO.sub.3                                                                             less than 0.03%                                         Reduced weight by reduction                                                                         less than 0.80%                                         Mean particle diameter                                                                              8.0 μm                                               ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Apparent density      0.4-0.7 g/cm.sup.3                                      Specific surface area 1.20 m.sup.2 /g                                         Purity                99.7% or more                                           Mean particle diameter                                                                              7.0 μm                                               ______________________________________                                    

EXPERIMENTAL EXAMPLE 1 Rust Preventing Effect

Copper powders shown in Tables 4 and 5 were respectively dispersed intoluene solvent by agitation, and were treated by adding surface coatingagents as shown in Tables 1, 2, and 3 in small portions to the copperpowder dispersed solutions. After drying the copper powders, their heatresistance and humidity resistance were evaluated by leaving them tostand for 1,350 hrs at a temperature of 85° C. or in an environment of45° C./95% RH. In these tests, the surface coating agents were usedrespectively in amounts of 0.05, 0.1, 0.5, 1.0, 3.0, 5.0, 10.0 and 10.5%by weight.

As a result, the copper powders according to this invention which hadbeen treated with the surface coating agents 1-1, 1-2, 1-3, 2-1, 2-2 and2-3 in amounts of 0.1 -10.5% by weight exhibited no change, andverdigris was not generated. Copper powders which had been treated withthe surface coating agents 1-4, 1-5, 1-6, 2-4, 2-5 and 2-6 in amounts of1.0-10.5% by weight became dark brown, but no generation of verdigriswas observed. On the other hand, copper powders which had been treatedwith the surface coating agents as shown in Table 3 acquired a darkbrown color with generation of verdigris. From these results, it isapparent that the copper powders according to this invention form densehydrophobic films and thus have excellent rust preventing effect andenvironmental resistance.

EXPERIMENTAL EXAMPLE 2 Volume Resistivity

The surface coated copper powders used in Experimental Example 1 wererespectively agitated with 45% by weight of an acrylic resin (solidcontent, 60% by weight) based on the weight of the respective copperpowder and with a solvent (toluene) for 10 min. by a homomixer toprepare conductive paints. Each of the obtained conductive paints wereformed into a circuit on an acrylate resin plate by the screen printingand dried in an atmosphere at 40° C. for 30 min. Volume resistivity ofeach circuit was measured.

It can be seen from the results that the conductive paints obtained fromthe copper powders according to this invention have volume resistivitiesof about 8×10⁻⁴ to 1×10⁻³ Ω·cm and thus have desirable conductivitiesand that they will not impair the conductivity.

EXPERIMENTAL EXAMPLE 3 Environmental Resistance of Paint Film

A conductor circuit was formed on an acrylate resin plate as describedin Experimental Example 2, and heat resistance and humidity resistancewere evaluated by respectively leaving the circuit to stand at 85° C.,40° C./95% RH for 1,350 hrs and measuring the rate of change inresistance (%). The surface coating agents used in this experiment were1-1, 1-2, 1-3, 2-1 , 3-1˜11.

As a result, most of the circuits obtained from the copper powders whichhad been treated with the surface coating agents 1-1, 1-2, 1-3 and 2-1,which were applied in amounts of 0.1-10.5% by weight, exhibited rates ofchange in resistance of ten and several percent, all of which werewithin the range of 7%-39%. On the other hand, when the surface coatingagents for comparison of 3-˜11 were used, most of the circuits exhibitedrates of chagne of 50 to 70%, some exceeding 100%.

From these results, it can be seen that the copper powder treated withthe mixture of the titanium acylate polymer and the higher carboxylicacid ester also has excellent aging resistance superior to those ofconventional metal organic compounds (titanium, silane or aluminum).

EXPERIMENTAL EXAMPLE 4 Environmental Resistance of Paint Film

A conductor circuit was formed on an acrylate resin plate as describedin Experimental Example 2, and environmental resistance was evaluated bya saline spraying test. The saline spraying test was carried out inaccordance with JIS (Japanese Industrial Standard) specifications, inwhich 5% by weight aqueous saline solution was used for spraying, and 72hours after spraying generation of verdigris was observed.

As a result, in non-treated copper powder, an extremely large amount ofverdigris was observed on the whole surface of the paint film, and inthe samples treated with the surface coating agents for comparison3-1˜11 verdigris was generated on about 50% of the paint film surface.On the other hand, in the case of the copper powders treated with thesurface coating agents 1-1 to 1-6 and 2-1 to 2-6 which were applied inamounts of 0.1 to 10.5% by weight, generation of verdigris was notobserved.

From these results, it can be seen that the copper powder treated withthe mixture of the titanium acylate polymer and the higher carboxylicacid ester is also superior in durability over those treated withconventional metal organic compounds (titanium, silane or aluminum).

EXPERIMENTAL EXAMPLE 5 Pull Strength

The conductive paints prepared in Experimental Example 2 were printed onacrylate substrates, polyester substrates, phenol substrates,glass-epoxy substrates, glass substrates, alumina-ceramics substrates byscreen printing to form 2×2 mm pad films, which were subjected to a 90°pulling test. The test was carried out by affixing a 0.5-mm diametertinned copper wire onto each paint film by using a cold setting epoxyresin. Each film had a thickness of 70±20 μm, and the amounts of thesurface coating agent were 0, 0.5, 1.0, 5.0 and 10.5% by weight inproportion to the weight of the copper powder.

The following results were obtained.

Acrylate substrates

While pull strength was 0.65 kg/mm² in the untreated samples, it was 0.8to 1.0 kg/mm² in most of the samples treated with the surface coatingagents 1-1 to 1-6 and 2-1 to 2-6, which were applied in amounts of 0.5to 10.5% by weight and was 0.5 to 0.6 kg/mm² in most of the samples forcomparison 3-1 to 3-11 regardless of the amounts of the surface coatingagents.

Polyester substrates

While pull strength was 0.58 kg/mm² in the untreated samples, it was 0.8to 1.0 kg/mm² in most of the samples treated with the surface coatingagents 1-1 to 1-6 and 2-1 to 2-6, which were applied in amounts of 0.5to 10.5% by weight and was 0.5 to 0.6 kg/mm² in most of the samples forcomparison 3-1 to 3-11 regardless of the amounts of the surface coatingagents.

Phenol substrates

While pull strength was 0.60 k9/mm² in the untreated samples, it was 0.9to 1.0 k9/mm² in most of the samples treated with the surface coatingagents 1-1 to 1-6 and 2-1 to 2-6, which were applied in amounts of 0.5to 10.5% by weight and was 0.5 to 0.6 kg/mm² in most of the samples forcomparison 3-1 to 3-11 regardless of the amount of the surface coatingagents.

Glass-epoxy substrates

While pull strength was 0.48 kg/mm² in the untreated samples, it was 0.9to 1.0 kg/mm² in most of the samples treated with the surface coatingagents 1-1 to 1-6 and 2-1 to 2-6, which were applied in amounts of 0.5to 10.5% by weight and was 0.5 to 0.6 kg/mm² in most of the samples forcomparison 3-1 to 3-11 regardless of the amount of the surface coatingagents.

Glass substrates

While pull strength was 0.38 kg/mm² in the untreated samples, it was 0.8to 1.0 kg/mm² in most of the samples treated with the surface coatingagents 1-1 to 1-6 and 2-1 to 2-6, which were applied in amounts of 0.5to 10.5% by weight and was 0.5 to 0.6 kg/mm² in most of the samples forcomparison 3-1 to 3-11 regardless of the amount of the surface coatingagents.

Alumina-ceramics substrates

While pull strength was 0.33 kg/mm² in the untreated samples, it was 0.8to 1.1 kg/mm² in most of the samples treated with the surface coatingagents 1-1 to 1-6 and 2-1 to 2-6, which were applied in amounts of 0.5to 10.5% by weight and was 0.5 to 0.6 kg/mm² in most of the samples forcomparison 3-1 to 3-11 regardless of the amount of the surface coatingagents.

FIG. 1 is an electron micrograph (×700) of a section of a dry film of aconductive paint (2×2 mm pad) prepared with the copper powder treatedwith the mixture of the titanium acylate polymer and the highercarboxylic acid ester (surface treatment agents 1-1 to 1-6 and 2-1 to2-6). It can be seen from the electron micrograph that the copper powderis homogeneously dispersed in the binder resin and that the substrateand the painted film are adhering strongly to each other.

FIG. 2 is an electron micrograph (×700) of a section of a dry film of aconductive paint (2×2 mm pad) prepared with the copper powder which hasbeen treated with the surface treatment agents 3-1 to 3-11. It can beseen from this electron micrograph that the copper powder is poorlydispersed in the binder resin and that the painted film is adheringweakly to the substrate because of unhomogeneous distribution of thecopper powder.

EXPERIMENTAL EXAMPLE 6 Pull strength

Pull strength was evaluated as in Experimental Example 5 except that thefollowing surface coating agents which contained no higher carboxylicester were used.

Surface coating agent 4-1: titanium acylate polymer obtained from 1 moleof tetraisopropyltitanium and 3 moles of isostearic acid (referred to asTAP1), and

Surface coating agent 4-2: titanium acylate polymer obtained from 1 moleof tetraisopropyltitanium and 3 moles of palmitic acid (referred to asTAP2).

In most of the experiments, pull strength remained at the level of 0.4to 0.6 kg/mm².

It is to be noted from the results of Experimental Examples 5 and 6, thecopper powders treated with the mixtures of the titanium acylate polymerand the higher carboxylic acid ester afford films which are far superiorin adhesion to conventional metal organic compounds (titanium, silane oraluminum).

EXPERIMENTAL EXAMPLE 7 Shielding effect

Conductive paints prepared in Experimental Example 2 were applied ascoating on acrylate matrixes by spraying method, and the electromagneticwave shielding effect of each film was evaluated at the initial stageand after aging of 1,350 hrs under a high temperature condition of 85°C. and high humidity condition of 40° C./95% RH by Advan test method.

The results were as follows.

Branch shaped copper powder, 500 MHz at initial stage: paint filmsobtained from the copper powder according to this invention (coatingagent Nos. 1-1 to 1-6 and 2-1 to 2-6) exhibited shielding effects of 54to 62 dB in the electric field, 52 to 64 dB in the magnetic field and 47to 56 dB in the distant field. On the other hand, films for comparison(coating agent Nos. 3-1 to 1-11) exhibited only low levels of shieldingeffects of 40 to 50 dB in the electric field, 39 to 46 dB in themagnetic field and 34 to 41 dB in the distant field.

Flake shaped copper powder, 500 MHz, at an initial: paint films obtainedfrom the copper powder according to this invention (coating agent Nos.1-1 to 1-6 and 2-1 to 2-6) exhibited shielding effects of 45 to 58 dB inthe electric field, 46 to 56 dB in the magnetic field and 41 to 52 dB inthe distant field. On the other hand, films for comparison (coatingagent Nos. 3-1 to 3-11) exhibited only low levels of shielding effectsof 35 to 39 dB in the electric field, 31 to 37 dB in the magnetic fieldand 39 to 36 dB in the distant field.

Branch shaped copper powder, 500 MHz after being left standing for 1,350hrs at a high temperature of 85° C.: paint films obtained from thecopper powder according to this invention (coating agent Nos. 1-1 to 1-6and 2-1 to 2-6 exhibited shielding effects of 42 to 54 dB in theelectric field, 41 to 54 dB in the magnetic field and 37 to 52 dB in thedistant field. On the other hand, films for comparison (coating agentNos. 3-1 to 3-11) exhibited shielding effects, which had been greatlylowered by aging to the level of 25 to 39 dB in the electric field, 25to 34 dB in the magnetic field and 23 to 31 dB in the distant field.

Branch shaped copper powder, 500 MHz after being left standing for 1,350hrs at a high humidity of 40° C./95% RH: paint films obtained from thecopper powder according to this invention (coating agent Nos. 1-1 to 1-6and 2-1 to 2-6) exhibited shielding effects of 44 to 58 dB in theelectric field, 45 to 58 dB in the magnetic field and 40 to 57 dB in thedistant field. On the other hand, films for comparison (coating agentNos. 3-1 to 3-11) exhibited shielding effects which had been greatlylowered by aging to the level of 29 to 39 dB in the electric field, 29to 34 dB in the magnetic field and 25 to 34 dB in the distant field.

Flake shaped copper powder, 500 MHz after being left standing for 1,350hrs at a high temperature of 85° C.: paint films obtained from thecopper powder according to this invention (coating agent Nos. 1-1 to 1-6and 2-1 to 2-6) exhibited shielding effects of 40 to 49 dB in theelectric field, 37 to 47 dB in the magnetic field and 34 to 45 dB in thedistant field, and thus they had undergone almost no deterioration byaging. On the other hand, films for comparison (coating agent Nos. 3-1to 3-11) exhibited shielding effects which had been extensively loweredby aging to the level of 19 to 25 dB in the electric field, 17 to 23 dBin the magnetic field and 17 to 22 dB in the distant field.

Flake shaped copper powder, 500 MHz after being left standing for 1,350hrs at a high humidity of 40° C./95% RH: paint films obtained from thecopper powder according to this invention (coating agent Nos. 1-1 to 1-6and 2-1 to 2-6) exhibited shielding effects of 42 to 52 dB in theelectric field, 41 to 52 dB in the magnetic field and 37 to 49 dB in thedistant field, and thus they had undergone almost no deterioration byaging. On the other hand, films for comparison (coating agent Nos. 3-1to 3-11) exhibited shielding effects which had been extensively loweredby aging to the level of 22 to 29 dB in the electric field, 21 to 28 dBin the magnetic field and 21 to 26 dB in the distant field.

It can be seen from the above results that the copper powder treatedwith the mixture of the titanium acylate polymer and the highercarboxylic acid ester affords a greatly improved shielding effectagainst electromagnetic waves as compared with conventional metalorganic compounds (titanium, silane or aluminum).

What is claimed is:
 1. A copper powder for electroconductive paints,comprising copper powder particles having a specific surface area of 1.5m² /g or less and a particle size distribution of 1 to 100 microns and amixture of a titanium acylate polymer and a higher carboxylic acid esterwhich has been applied as a coating on the surfaces of said particles.2. A copper powder for electroconductive paints according to claim 1wherein said higher carboxylic acid ester is a fatty acid ester having10 to 24 carbon atoms.
 3. A copper powder for electroconductive paintsaccording to claim 1, wherein said titanium acylate polymer hasrepeating units represented by at least one of the following forumlae I,II and III: ##STR3## wherein R, R₁, R₂ and R₃ may be the same ordifferent and represent hydrocarbon groups having 1 to 25 carbon atoms.4. A copper powder for electroconductive paint according to claim 1wherein the titanium acrylate polymer forms a film on the surface of thecopper particles, said film having spaces therein, and a film of saidhigher carboxylic acid ester formed within said spaces in the film ofsaid titanium acrylate polymer.